CN105839061A - NiCoCrAlY / ZrO2 composite coating on gamma-TiAl alloy surface and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of titanium alloy surface treatment. The NiCoCrAlY / ZrO2 composite coating comprises a ZrO2 alloying layer, a NiCoCrAlY layer and a NiCoCrAlY diffusion layer from a surface layer to an inner layer. The invention adopts the double glow plasma surface alloying technology to form the NiCoCrAlY alloying layer on the surface of gamma-TiAl alloy surface; then oxygen is introduced for ZrO2 co-alloying to form a ZrO2 alloying layer on the surface of NiCoCrAlY coating; finally a high temperature oxidation-resistant NiCoCrAlY / NiCoCrAlY composite layer is formed on the surface of gamma-TiAl titanium alloy. The ZrO2 alloying layer endows the gamma-TiAl titanium alloy with sufficient high temperature protection ability, the sub-surface NiCoCrAlY alloying layer can overcome the serious decomposition of ZrO2 coating under high temperature; and the NiCoCrAlY / ZrO2 multilayer structure realizes sufficient and reliable bonding strength between the alloy layer and a matrix, so as to improve the high temperature oxidation resistance and wear resistance of the gamma-TiAl alloy.

Description

NiCoCrAlY/ZrO2 Composite Coating on γ-TiAl Alloy Surface and Its Preparation Method

technical field

The invention belongs to the field of titanium alloy surface treatment, in particular to a NiCoCrAlY/ZrO2 composite coating _on the surface of a gamma-TiAl alloy and a preparation method thereof.

Background technique

In order to increase the thrust-to-weight ratio of aerospace vehicle engines and save fuel, it is an important method to increase the working temperature of materials and reduce their structural weight. The Ti-Al intermetallic compound has high specific strength, and its high-temperature strength and rigidity are higher than those of Ni-based and Ti-based alloys. It is internationally recognized as the most potential high-temperature structure in materials for aviation, aerospace vehicle engines, industrial gas turbines, and automotive engines. One of the materials, it has attracted the attention of scientists and relevant departments at home and abroad. Among the Ti-Al intermetallic compounds, Ti ₃ Al, TiAl and TiAl ₃ are the most widely studied. Among them, the γ-TiAl alloy is a hotspot of extensive research at home and abroad, and it has developed rapidly and has entered the application stage.

γ-TiAl is a typical Berthollide-type compound with a wide composition range, from 48% (atomic) Al to 69.5% (atomic) Al, and is stable at temperatures below the melting point (~1465 ° C), with outstanding thermophysical and Thermochemical stability, which mainly depends on the structural properties of the compound that is ordered at any temperature and the direction bonds of the compound. γ-TiAl-based alloys not only have the characteristics of high temperature resistance, oxidation resistance and low density, but also have better elastic modulus and creep resistance than Ti-based alloys, even better than α ₂ -Ti ₃ Al-based alloys. It is equivalent, but its density is less than half of that of Ni-based alloys. Its service temperature can reach above 900°C, and its elastic modulus at room temperature can reach as high as 176GPa, and it decreases slowly with the increase of temperature. These performance advantages fill the gaps in the use of high-temperature Ti-based alloys and Ni-based superalloys, and are considered to be one of the new lightweight high-temperature structural materials with great application prospects, especially for future aerospace, engines and gas turbines. force.

However, at high temperatures exceeding 800 °C, the oxidation resistance of γ-TiAl alloys drops sharply, because the free energy of formation of TiO ₂ and Al ₂ O ₃ is closer, and the formation rate of TiO ₂ is faster than that of Al ₂ O ₃ Speed, the _TiO2 oxide film has a loose layered structure, so a complete and dense protective oxide film cannot be formed on the surface of the TiAl alloy. Due to the infiltration of N and O atoms at high temperature, the alloy is prone to subsurface embrittlement, which leads to a significant decrease in the mechanical properties of γ-TiAl alloys such as thermal stability, durability strength, creep resistance and fatigue strength. At the same time, the tribological properties of γ-TiAl alloy are poor, and there are serious tendency of adhesive wear and fretting wear.

Thermal barrier coating refers to a coating system composed of a metal buffer layer or a metal bonding layer and a ceramic surface coating. It is currently widely used in the field of surface protection of high-temperature components. He Bo et al. from Shanghai Jiaotong University prepared NiCoCrAlY+8YSZ thermal barrier coating on the surface of titanium alloy by EB-PVD (Journal of Aeronautical Materials, 2007,27(4):25-30.), the coating is dense and uniform, with high hardness, The thermal insulation performance is good, but the operation is complicated, the deposition efficiency is low, and the technology is difficult; people such as Pan Zhaoyi of Xi'an Aerospace Engine Factory use atmospheric plasma spraying to prepare NiCrAlCoY+8YSZ coating on the surface of stainless steel (Rocket Propulsion, 2013,39 (6): 48 -54.), the coating has high bonding strength, good heat insulation effect, good wear resistance, and excellent thermal shock resistance at high temperatures, but the thickness of the coating is uncontrollable and the mechanical bonding with the substrate is poor. Easy to fall off during use. Therefore, how to improve the high temperature oxidation resistance and wear resistance of the titanium alloy surface has always been a technical problem to be solved in this field.

Contents of the invention

Aiming at the problems of high-temperature oxidation resistance, tribological properties and poor bonding force existing in the prior art, the present invention provides a NiCoCrAlY/ZrO ₂ composite coating on the surface of γ-TiAl alloy and its preparation method, which improves the γ-TiAl alloy surface. High-temperature oxidation and wear resistance of TiAl alloy surfaces.

The present invention adopts the following technical scheme: a NiCoCrAlY/ZrO composite coating _on the surface of a gamma _- TiAl alloy, which is characterized in that, the composite coating is ZrO infiltrated layer, NiCoCrAlY deposited layer, NiCoCrAlY deposited layer, NiCoCrAlY diffusion layer.

Further, the thickness of the ZrO ₂ infiltrated layer is 3-5 μm, and the content of Zr and O in the ZrO ₂ infiltrated layer decreases gradually from the surface layer from the outside to the inside.

Further, the thickness of the NiCoCrAlY deposition layer is 4 to 6 μm, the content of Ni, Co, Cr, and Y remains stable in the range of the NiCoCrAlY deposition layer, and the content of Ti and Al elements in the NiCoCrAlY/ _ZrO2 composite coating is from the surface layer to the surface layer. increasing within.

Further, the thickness of the NiCoCrAlY diffusion layer is 2-4 μm, the content of Ni, Co, Cr and Y in the NiCoCrAlY diffusion layer decreases continuously from the surface layer to the inside, and the content of Ti and Al in the NiCoCrAlY diffusion layer from the surface layer to the inside shows a The gradient increases until it stabilizes.

The present invention also adopts the following technical scheme: the preparation method of a NiCoCrAlY/ZrO2 composite coating _on the surface of a γ-TiAl alloy according to the present invention, which is characterized in that it is prepared on the surface of the γ-TiAl alloy by using double glow plasma metallization technology NiCoCrAlY infiltrated layer, and then pass in oxygen, carry out Zr-O co-infiltrated, form a layer of ZrO ₂ infiltrated layer on the surface of NiCoCrAlY coating, and finally form a layer of NiCoCrAlY/ZrO ₂ composite with high temperature oxidation resistance on the surface of γ-TiAl alloy Coating, the steps are as follows:

(1) Put the γ-TiAl alloy and NiCoCrAlY alloy target into the double-layer glow plasma surface alloying device, and use the NiCoCrAlY alloy target as the source;

(2) Vacuumize, fill with argon, start the glow, and the process parameters for debugging are:

The distance between the target and the workpiece is 15-20mm

Working pressure: 30-35Pa

Source voltage: 900-1000V

Workpiece voltage: 400-450V

Temperature: 900-1000℃

Holding time: 3.5-4.5h;

(3) reduce the voltage to zero, extinguish the glow, turn off the power supply, pump to the ultimate vacuum, and cool to room temperature to obtain the NiCoCrAlY deposition layer;

(4) Replace the pure Zr target as the source, vacuumize, pass argon and oxygen, adjust the flow ratio of argon and oxygen to (5-10):1, and perform Zr-O co-infiltration on the surface of the NiCoCrAlY alloy infiltration layer , to complete the preparation of the ZrO ₂ infiltration layer, the debugging process parameters are:

Distance between target and workpiece: 10-15mm

Working pressure: 35-45Pa

Source voltage: 850-950V

Workpiece voltage: 400-450V

Temperature: 800-900°C

Holding time: 2-3h;

(6) Reduce the voltage to zero, extinguish the glow, adjust the flow of argon and oxygen to zero, disconnect the power supply, and complete the preparation of the NiCoCrAlY/ZrO ₂ composite coating.

The present invention has following beneficial effect:

(1) The ZrO ₂ coating prepared by double-glow Zr-O co-infiltration is dense and uniform without holes, and it is metallurgically bonded with the NiCoCrAlY infiltration layer, with high bonding strength, which endows the γ-TiAl alloy with sufficient high temperature protection ability.

(2) The NiCoCrAlY infiltrated layer on the subsurface can effectively delay the diffusion of coating element atoms into the matrix during long-term high-temperature service, and overcome the serious problem of ZrO ₂ coating decomposition under high-temperature conditions. Under the environment, the Al in the NiCoCrAlY bonding layer will diffuse outward, and selectively oxidize on the surface of the coating to form a dense Al ₂ O ₃ protective film to prevent further oxidation of the bottom layer, thereby achieving the purpose of protecting the substrate. _The ZrO2 phase with high surface hardness can improve the wear resistance of the alloy.

(3) The multilayer structure of NiCoCrAlY/ZrO ₂ can endow it with better adhesion and fatigue resistance, and the composition, structure and performance of the inner alloy layer change in a gradient, so that there is a strong bond between the alloy layer and the substrate. Adequate and reliable bond strength.

Description of drawings:

Fig. 1 is the surface morphology diagram of the NiCoCrAlY/ZrO ₂ composite coating prepared in the present invention.

Fig. 2 is a cross-sectional morphology diagram of the NiCoCrAlY/ZrO ₂ composite coating prepared in the present invention.

detailed description

The technical solutions of the present invention will be further elaborated below in conjunction with the accompanying drawings and specific embodiments.

Example 1

(1) After cutting the γ-TiAl alloy into a sample of 15×15×5mm, the surface of the sample was first polished with sandpaper, then polished to a mirror surface with Cr ₂ O ₃ polishing powder, and finally ultrasonically cleaned in alcohol;

(2) Place NiCoCrAlY (composition Ni-(20～23)Co-(20～24)Cr-(11～13)Al-(0.25～0.45)Y) at the source of the double-layer glow plasma metallization furnace and pure Zr (purity 99.99%) target, the size is Before loading into the furnace, the target material needs to be polished with sandpaper to expose the fresh surface, ultrasonically cleaned with anhydrous ethanol, and dried;

(3) The γ-TiAl alloy sample is placed on the stage, parallel to the target, the distance between the NiCoCrAlY alloy target and the γ-TiAl alloy sample is controlled at 15-20mm, and then the bell jar is lowered;

(4) Turn on the mechanical pump to evacuate to below 5pa, pass in argon, adjust the air pressure in the furnace to 35pa, turn on the source voltage and workpiece voltage, slowly adjust, start, and finally control the source voltage and workpiece voltage at 950V and 450V, and wait for the temperature in the furnace to reach 1000°C, after holding for 4 hours, stop the glow, and disconnect the power supply, so as to obtain the NiCoCrAlY deposition layer;

(5) Open the device, take out the NiCoCrAlY alloy target, replace it with a pure Zr target as the source, close the device, and put in argon and oxygen after vacuuming, adjust the electrode spacing to 10mm, and the flow ratio of argon and oxygen to 5:1 , the source voltage is adjusted to 900V, the workpiece voltage is adjusted to 400V, the temperature in the furnace is controlled at 900°C, the working pressure is adjusted to 40Pa, the holding time is 3h, and the Zr-O co-infiltration is carried out on the surface of the NiCoCrAlY alloy infiltration layer to complete the ZrO ₂ infiltration layer preparation of

(6) Reduce the voltage to zero, turn off the glow, adjust the flow of argon and oxygen to zero, disconnect the power supply, and complete the preparation of the NiCoCrAlY/ZrO ₂ composite coating.

The prepared coating was tested for hardness, the specific test method is as follows:

Testing equipment: SHIMAZU M84207 microhardness tester made in Japan;

The specific operation method is as follows: first put the sample into alcohol and ultrasonically clean it, then put it on the stage, use a 400 times microscope to observe the surface of the sample, determine the location of hardness measurement, then automatically load 100g for 15 seconds, and calibrate the indentation The length of the diagonal line, print out the hardness value, and take the average value of the three points of the test. The average surface hardness of the NiCoCrAlY/ZrO ₂ composite layer is 1279HV _0.1 , and the average hardness of the γ-TiAl matrix is 357HV _0.1 . Compared with the two, the coating hardness much larger than the substrate. The test results are shown in Table 1:

Table 1 Hardness of NiCoCrAlY/ZrO ₂ composite coating

The wear resistance of the NiCoCrAlY/ZrO ₂ composite coating was evaluated by using the ball-on-disk friction and wear test. The specific test method is as follows:

Test equipment: HT-500 high temperature friction and wear testing machine;

The specific operation method is as follows: first put the sample into alcohol and ultrasonically clean it, then fix the sample in the friction disc, choose Si ₃ N ₄ ceramic balls with a diameter of 4.763mm (75-80HR) as the counter-grinding material. The grinding radius is 2mm, the test load is 330g, the rotational speed is 560r/min, the wear time is 30min, and the test temperature is 20±5°C. Before and after the experiment, an electronic balance with an accuracy of 0.1mg is used to weigh the mass loss of the sample before and after wear. In the friction and wear experiment, the friction coefficient of the coating is compared with that of the substrate, and the hardness of Si ₃ N ₄ to the grinding ball is also much greater than that of the substrate. During the friction process, the depth of the ball pressed into the surface of the substrate is relatively deep, and the resistance it receives is relatively large , which leads to an increase in the coefficient of friction; while the hardness of the coating is not much different from that of the counter ball, the indentation depth is shallow, and the resistance received is small, so the coefficient of friction is low. The test results are shown in Table 2:

Table 2 NiCoCrAlY/ZrO ₂ composite coating wear resistance test results

To evaluate the high temperature oxidation resistance of NiCoCrAlY/ZrO ₂ composite coating, the specific test method is as follows:

Test equipment: high temperature muffle furnace;

The specific operation method is as follows: first put the sample into alcohol and ultrasonically clean it, then put the sample into the muffle furnace, adjust the temperature to 750°C, 850°C, 950°C, keep it warm for 100h, take it out every 20h, and let it cool naturally Finally, the weight of the sample was weighed with an electronic balance with an accuracy of 0.1 mg, and the oxidation weight gain was obtained. In the experiment at 750 ° C, the surface of the substrate began to peel off after 60 hours. At 950°C, the substrate was destabilized and oxidized, and the surface was completely peeled off. However, at 750°C, 850°C and 950°C, the surface of the coating was intact after 100 hours without peeling off. The test results are shown in Table 3:

Table 3 NiCoCrAlY/ZrO ₂ composite coating high temperature oxidation resistance test results

NiCoCrAlY/ZrO that the present invention makes Composite coating surface topography figure, see specification sheet Fig. ₁ ;

The NiCoCrAlY/ZrO ₂ composite coating obtained in the present invention is shown in Figure 2 of the description.

Example 2

Except that the parameters of Zr-O co-infiltration are changed to working pressure of 45Pa, source voltage of 950V, cathode voltage of 450V, pole spacing of 15mm, argon and oxygen flow ratio of 10:1, and heat preservation for 2 hours, other steps are the same as in Example 1 .

In the room temperature friction and wear test of this embodiment, the friction coefficient of the coating is 0.28, and the wear amount is 0.57mg, which is 77.01% lower than that of the substrate. The high temperature oxidation tests at 750°C, 850°C, and 950°C show that the coating After 100 hours, it is well bonded to the substrate, no peeling occurs on the surface, the oxidation weight gain is 25 mg/cm ² , which is further lower than that in Example 1, and the oxidation resistance is good.

Claims (5)

1. NiCoCrAlY/ZrO _on a γ _- TiAl alloy surface Composite coating, it is characterized in that, described composite coating is ZrO successively from surface layer from outside to inside percolation layer, NiCoCrAlY deposition layer, NiCoCrAlY diffusion layer. 2. the NiCoCrAlY/ZrO on the γ-TiAl alloy surface according to claim 1 ₂ composite coatings, it is characterized in that, described ZrO ₂ infiltrated layer thickness is 3 ~ 5 μ m, and the content of Zr, O is more _than ZrO infiltrated layer Gradient descent from the surface layer from outside to inside. _3. the NiCoCrAlY/ZrO composite coating on γ-TiAl alloy surface according to claim 1, it is characterized in that, described NiCoCrAlY deposition layer thickness is 4～6 μ m, Ni, Co, Cr, Y content are in NiCoCrAlY The content of the deposition layer remains stable, and the content of Ti and Al elements in the NiCoCrAlY/ZrO ₂ composite coating increases from the surface layer to the inside. 4. the NiCoCrAlY/ZrO composite coating on the γ-TiAl alloy surface according to claim ₁ , is characterized in that, described NiCoCrAlY diffusion layer thickness is 2～4 μm, Ni, Co, Cr, Y content are in NiCoCrAlY The diffusion layer decreases continuously from the surface layer to the inside, and the Ti and Al contents in the NiCoCrAlY diffusion layer gradually increase from the surface layer to the inside until they are stable. 5. as the arbitrary described NiCoCrAlY/ZrO of claim 1-4 alloy surface _The preparation method of the composite coating is characterized in that, first utilizes double glow plasma metallization technology to prepare NiCoCrAlY infiltrated on the γ-TiAl alloy surface layer, and then feed oxygen, carry out Zr-O co-infiltration, form a layer of ZrO ₂ infiltration layer on the surface of NiCoCrAlY coating, and finally form a layer of NiCoCrAlY/ZrO ₂ composite coating with high temperature oxidation resistance on the surface of γ-TiAl alloy ,Proceed as follows: (1) Put the γ-TiA alloy and NiCoCrAlY alloy target into the double-layer glow plasma surface alloying device, and use the NiCoCrAlY alloy target as the source; (2) Vacuumize, fill with argon, start the glow, and the process parameters for debugging are: The distance between the target and the workpiece is 15-20mm Working pressure: 30-35Pa Source voltage: 900-1000V Workpiece voltage: 400-450V Temperature: 900-1000℃ Holding time: 3.5-4.5h; (3) Reduce the voltage to zero, turn off the glow, turn off the power, pump to the ultimate vacuum, and cool to room temperature to obtain a NiCoCrAlY deposition layer; (4) Replace the pure Zr target as the source, vacuumize, pass argon and oxygen, adjust the flow ratio of argon and oxygen to (5-10):1, and perform Zr-O co-infiltration on the surface of the NiCoCrAlY alloy infiltration layer , to complete the preparation of the ZrO ₂ infiltration layer, the debugging process parameters are: Distance between target and workpiece: 10-15mm Working pressure: 35-45Pa Source voltage: 850-950V Workpiece voltage: 400-450V Temperature: 800-900°C Holding time: 2-3h; (6) Reduce the voltage to zero, turn off the glow, adjust the flow of argon and oxygen to zero, disconnect the power supply, and complete the preparation of the NiCoCrAlY/ZrO ₂ composite coating.